1. Field of the Invention
The present invention relates to pipe couplings and, more particularly, to repeatedly disconnectable and reconnectable threaded pipe couplings for high pressure lines featuring an annular gasket under compression inside a gasket chamber as a sealing element.
2. Description of the Prior Art
A number of different pipe couplings, including pipe couplings adapted for either pressure line applications or vacuum line applications, or both, are known from the prior art. Many of these couplings are not suitable for repeated disconnection and reconnection, because they rely on a permanent deformation of a coupling component to produce the required seal.
It has therefore already been suggested to use an elastically deformable and/or compressible annular gasket in a threaded pipe coupling, in order to produce a reliable seal between the mating coupling components which can be released and reestablished.
Two threaded pipe couplings featuring an annular gasket are disclosed in German Pat. No. 363 983 and in U.S. Pat. No. 3,615,109. Both pipe couplings produce a reliably sealed pipe union and both are readily reconnectable after disconnection. Depending on circumstances, it may be advantageous to replace the annular gasket prior to reconnection. Both of these known pipe couplings also have cooperating radial shoulders on their coupling components, for the axial force transfer from one coupling component to the other, thus meeting the highest demands of tightness and mechanical resistance to axial separation.
However, these known pipe couplings have a common shortcoming, inasmuch as, for the accommodation of the annular gasket, the two pipe ends must be fitted with permanently attached special end pieces which cooperate to form a chamber inside which the gasket is compressed.
In the case of German Pat. No. 363 983, the gasket chamber is of trapezoidal shape, being constituted by two parallel opposing radial pressure faces on the two end pieces, a slightly conical bore in one end piece and an oppositely tapered extension on the other end piece. The radial pressure faces reach beyond the radial width of the gasket, so that each pressure face comes to bear against an abutment face of the opposite end piece in the connected position. The result is a predetermined size of the gasket chamber in the connected position. The annular gasket has to have a comparable trapezoidal cross section.
In the case of U.S. Pat. No. 3,615,109, the annular gasket is an O-ring, the gasket chamber consisting of an interior annular groove in on of the two end pieces, the proximate flank of the groove being truncated by a conical interior face which cooperates with a matching conical exterior face on the extremity of the opposite end piece. The latter thus penetrates into the gasket chamber in the connected position, until the two conical faces abut against each other, thereby producing a triangular gasket chamber. As a result, the cross section of the O-ring is deformed from its circular shape into a triangular shape.
Both prior art solutions have the additional shortcoming of offering no protection against pinching of the gasket, or, under extreme pressure conditions, the extrusion of the gasket into the gaps between the surfaces which form the gasket chamber.
Lastly, neither of these two pipe couplings is adaptable for use as a coupling between a pipe and a wall port of the kind which are found in cylinder assemblies, valve blocks and other types of housings.
Another known pipe coupling with annular gaskets, intended for use in high vacuum equipment, is disclosed in British Pat. No. 904,566. This pipe coupling suggests the use of two O-rings which are confined inside, and deformed by, triangular gasket chambers, in a configuration in which the walls of each gasket chamber are constituted by the outer diameter of the end portion of one of the two pipes, a conical recess or chamfer in a flanged sleeve or tail which is soldered to the pipe end portion, and a spacer ring which receives and centers the two pipe end portions while abutting against the flanged sleeves. This abutment determines the size of the triangular gasket chambers.
Since this pipe coupling is designed for vacuum applications only, the problems of potential gasket extrusion and of preventing an axial separation of the coupling components do not exist. The suggested pipe coupling is not suitable for use as a high-pressure pipe coupling.
The German Gebrauchsmuster (Utility Model) No. 1 535 786 discloses a pipe coupling featuring an annular gasket of copper or leather which is confined between the planar end faces of two pipes and the bore of a central sleeve receiving the end portions of the two pipes. This coupling can also be used for the attachment of a pipe to a wall port, in which case the pipe end portion is received in a recessed bore.
The axial clamping attachment is obtained by means of two threaded sleeves--a single threaded sleeve in the case of a wall port--which surround the pipe end portions. Two snap rings which are engaged in shallow grooves on the outer side of the pipe end portions and protrude into recesses of the threaded clamping sleeves transmit the axial clamping force from the clamping sleeves to the pipe end portions.
This pipe coupling differs from the previously described pipe couplings, inasmuch as the gasket is not surrounded by a gasket chamber, but is confined on only three of the four sides of a rectangle. It follows that this pipe coupling can withstand only limited internal pressure.
Heretofore, the most widely used pipe coupling for high pressure hydraulic lines has been a pipe coupling which uses a thin-walled, slightly tapered metallic sleeve which is forced into a matchingly tapered bore of an opposing coupling component, so as to be deformed to a smaller diameter. The metallic sleeve has a bore with two shallow grooves near its leading edge forming a succession of three interior annular cutting edges which, as the sleeve is advanced and radially deformed, successively penetrate the outer surface of the pipe end portion to create angled annular grooves, for a reliable axial force transmission from the associated threaded coupling component to the pipe. The creation of the first angular groove, which is the deepest of the three, simultaneously produces a small annular ridge ahead of the groove which is forced against the tapered bore of the opposing coupling component for a reliable metal-to-metal seal.
This pipe coupling is most effective as initially assembled. While it is possible to disconnect and reconnect this coupling, the quality of the reconnected pipe coupling is always inferior, due to the absence of the virgin metal deformation which takes place during the first clamping operation, as described above.